The present invention is directed to a dental handpiece which has at least two handpiece parts, each having a drive shaft and a cooling line segment for at least one cooling agent, connecting means for releasably interconnecting the two parts with gears of the drive shafts in driving engagement enabling said connecting means including means for preventing relative twisting between the two handpiece parts including a guide fitting strip arranged on one of the handpiece parts and extending axially therefrom to be engaged in an axially extending guide slot in the other handpiece part.
For the axial connection of two handpiece parts, it is known to align these parts in their desired angular position with respect to one another with the assistance of a pin engaged in a longitudinal slot or bore and to then connect the two handpiece parts to one another by means of a coupling sleeve. In this construction, the cooling agent line sections or segments are formed by means of exposed hoses which are arranged along the outside of the handpiece parts. This type of connection involves too much time for a quick interchange of handpiece parts.
Another type of dental handpiece construction is disclosed in German O.S. No. 2,802,325. In this device, the connecting means contains the slotted sleeve and a recess arranged diametrically offset with respect thereto on the circumference of the one handpiece part. The other handpiece part has projections fitting into the slot. The sleeve and the mandrel exhibit elastic deformable parts, which after axial insertion of the mandrel into the sleeve slot allow the mandrel projections to engage in the sleeve recess and hold it locked therein after subsequent twisting of the two handpiece parts along the longitudinal axis. The connection and sealing of the two coolant line ends at the coupling location are obtained via a ring seal between the abutting end faces of the two handpiece parts. The height or the axial length of the ring seals is somewhat greater than the axial depth of the bore in which the ring seal is inserted so that the ring seal projects slightly above the one end face in the uncoupled state and a surface seal with a specific surface pressure is achieved in the coupled state.
So that a tight connection of the cooling agent line sections is guaranteed, a relatively great surface pressure must be generated which in the final analysis leads to the bayonet type connection of the two handpiece parts to be relatively tight. Since the seal is loaded for shearing or respectively torsion at practically every coupling and uncoupling operation, relatively high wear of this seal will occur with this type of structure.
For solving the problems of conveying a cooling line agent between two handpiece parts, it is also known to secure to the one handpiece part a cooling agent line section in the form of a rigid tube with an excessive length corresponding approximately to the length of the other handpiece part. When the other handpiece part is removed, the cooling agent line section allocated to the other handpiece part remains on the one handpiece part and projects therefrom. Given such an arrangement however, there is a danger that the relatively thin cooling agent lines will be bent or damaged in some other manner and that exact recoupling is thus no longer guaranteed.